Add single areaset to both areasets when Node not on edge
If we don't do this, we can't tell the difference between a node on the
edge of an area, which can connect to nodes outside sharing the default
areaset, with nodes inside which would also contain the default areaset.
Thus, add the inside area to both "directions" (left/right, up/down,
although neither applies) so we can't connect to nodes outside the area.